Machines for folding paper and other sheets

ABSTRACT

A machine for folding a sheet with a concertina fold comprises a pair of rotary creasing devices each of which includes an axially extending male creasing member and an axially extending female creasing member arranged so that on rotation of the devices the male and female members of the two devices mate with each other alternately and produce creases alternately in opposite directions in a sheet which is fed freely between the creasing devices by a feeding mechanism. The speed by which the sheet is fed by the feeding mechanism is adjustable and the speed of rotation of the creasing devices is constant so that the space between adjacent creases can be adjusted by adjusting the speed of the feed mechanism. Each of the male creasing members consists of an axially extending blade and each of the female members comprises a pair of rollers forming a nip between them into which the sheet is pushed by the blade of the other device as the devices rotate. The rollers are rotated contra to each other to draw the sheet into the nip between them to form the crease and subsequently the direction of rotation of the rollers is reversed so that the part of the sheet held between the rollers is discharged again after the crease has been formed.

United States Patent 5] Mar. 7, 1972 Kemp [54] MACHINES FOR FOLDING PAPER AND OTHER SHEETS [72] Inventor: Jack Voyna Leslie Kemp, Toddington,

Dunstable, England [73] Assignee: Kemp Applications Limited, Dunstable,

England [22] Filed: Jan. 15, 1970 [21] Appl. No.2 3,022

[30] Foreign Application Priority Data Feb. 21, 1969 Great Britain ..9,566/69 [56] References Cited UNITED STATES PATENTS 6/1922 11/1926 ll/l943 11/1952 Ellis ..270/86 X 3,266,794 8/1966 Weir ..270/81 Primary Examiner-Robert W. Michell Assistant Examiner-R. P. Dyer Attorneyl'lolcombe, Wetherill & Brisebois [57] ABSTRACT A machine for folding a sheet with a concertina fold comprises a pair of rotary creasing devices each of which includes an axially extending male creasing member and an axially extending female creasing member arranged so that on rotation of the devices the male and female members of the two devices mate with each other alternately and produce creases alternately in opposite directions in a sheet which is fed freely between the creasing devices by a feeding mechanism. The speed by which the sheet is fed by the feeding mechanism is adjustable and the speed of rotation of the creasing devices is constant so that the space between adjacent creases can be adjusted by adjusting the speed of the feed mechanism. Each of the male creasing members consists of an axially extending blade and each of the female members comprises a pair of rollers forming a nip between them into which the sheet is pushed by the blade of the other device as the devices rotate. The rollers are rotated contra to each other to draw the sheet into the nip between them to form the crease and subsequently the direction of rotation of the rollers is reversed so that the part of the sheet held between the rollers is discharged again after the crease has been formed.

9 Claims, 5 Drawing Flgures PATENTEDMAR 71912 3,647,201

SHEET lUF 3 PATENTEDMAR 1 I972 sum 2 0F 3 iwm . QSL QQ E PATENTEDMAR 7 I972 3, 647. 201

SHEET 3 OF 3 MACHINES FOR FOLDING PAPER AND OTHER SHEETS This invention relates to machines for folding paper and other sheets of a substantial size, for example prints of engineering drawings or maps.

Machines are already available which will fold large paper sheets such as prints of engineering drawings to a predetermined size, but with these machines it is necessary to set the machine according to the size of the sheet which is to be fed to it and it is necessary therefore to collate the sheets beforehand so that a batch of sheets all of the same size can be fed to the machine one after another.

Other folding machines are available in which this presetting is not necessary and these comprise a pair of feed and creasing rollers which form a nip between them and each of which has an axially extending male creasing blade and a female creasing groove arranged diametrically opposite each other. As the two rollers rotate in opposite directions to each other and a sheet is fed between them, the blade on one roller enters the groove in the other roller with the sheet trapped between them and a crease is formed across the sheet in one direction. When the rollers have rotated through a further half revolution, the blade on the other roller enters the groove on the one roller and a further crease is formed in the sheet in an opposite direction to the first crease. As the rollers continue to rotate a series of creases are produced in opposite directions so that the sheet is folded in a zigzag or concertinalike manner.

This form of machine has proved quite satisfactory, but it suffers from the disadvantage that the length of sheet fed by the rollers between each successive entry of a blade into its slot is constant and cannot be varied so that the creases are produced at constant intervals and the folded size of the sheet cannot therefore be varied.

The aim of the present invention is to provide a machine which will fold a sheet with a concertina fold of the nature just described, but in which the distance between adjacent creases can be varied to vary the folded size of the sheet.

To this end, according to this invention, such a machine comprises a feed mechanism for feeding sheets to be folded and a pair of rotary creasing devices each of which includes an axially extending male creasing member and an axially extending female creasing member arranged so that on rotation of the devices the male and female members mate with each other in turn and produce creases alternately in opposite directions in a sheet which is fed between the devices by the feeding mechanism, the spaces between the creases being de pendent on the rate of feed of the sheet, which is determined by the feed mechanism, relative to the rate of rotation of the devices and these rates being adjustable relative to each other.

With this arrangement in which the feeding of the sheet in between the creasing devices is independent of the rate of rotation of the devices themselves, the spacing of the creases can readily be altered so that the size of the concertina folded sheet can be adjusted as required regardless of the dimension of the sheet in the direction in which it is fed. Further, the machine will accept successive sheets of different dimensions in the direction of feed and fold them to the same size as each other measured across the folds without any adjustment of the machine between the acceptance of the successive sheets being necessary.

The male and female creasing members may consist of an axially extending blade and an axially extending groove respectively as in the earlier machine provided with rollers, but instead of providing the blade and the groove on rollers, they are mounted on a support which is arranged to rotate about an axis and carries the blade and the groove at equal distances from this axis, but the supports of the two creasing devices have no parts which come into engagement with each other other than the blades and narrow axially extending parts in which the grooves are formed.

Preferably, however, the female member instead of consisting merely ofa part formed with a groove, consists ofa pair of rollers forming a nip between them. These rollers are of small diameter compared with the diameter of the pitch circle around which they move as the creasing device rotates and the nip which they form between them extends parallel to the axis of rotation of the device. As the two devices rotate, the blade on one device pushes the sheet into the nip formed between the two rollers on the other device and subsequently the blade on the other creasing device pushes the sheet into the nip between the rollers on the first creasing device.

The creasing rollers forming the female member of each creasing device may be idle and resiliently mounted so that the crease is merely pushed into the nip formed between them by the blade as the two members mate and the sheet is subsequently pulled out from the nip as the rotation of the device continues and the next crease is formed, but preferably the rollers are provided with an intermittent driving mechanism which causes them to rotate contra to each other through a small angle to draw the sheet into the nip formed between them as the rollers on one creasing device mate with the blade on the other device and subsequently the rollers are caused to rotate in opposite directions to release the creased sheet prior to the formation ofthe subsequent crease.

An example of a machine constructed in accordance with the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a side view with parts broken away and other parts shown in section to illustrate internal details;

FIG. 2 is a plan view also'with parts broken away to show details and with other parts indicated only in outline; and,

FIGS. 3a, 3b and 3c are somewhat diagrammatic side views of the rotary creasing devices showing these at three successive stages of their operation.

The machine has a casing l with sideplates 2 and 3, end plates 4 and 5 and a bottom 6 which together form a frame supporting the moving parts of the machine. The casing l is supported on legs 7 only parts of which are shown in FIG. 1.

Near the top of the casing l is a feed mechanism comprising a paper feed table in two sections 8 and 9. Above the righthand end of the section 8 of the table and above the section 9 is a guide plate 10 provided with various slots. The plate 10 is supported from crossmembers 11 and 12 which extend between the sideplates 2 and 3 and thus also help to stiffen the casing 1.

The section 9 of the feed table has the upper flights of four conveyor belts 13 extending along it. The conveyor belts 13 extend round an idle roller 14 and a driving roller 15 which are supported in bearings 16 and I7 respectively on the sideplates 2 and 3v The driving roller 15 has a shaft 18 which extends through the sideplate 2 and carries a chain sprocket 19. The driving roller 15 is driven by a constant speed electric motor 20 which is mounted on the end plate 5 through driving chains 21, 22 and 23. The chain 21 drives an input sprocket 24 of an infinitely variable speed gear 25 and the chain 22 is driven by an output sprocket 26 of the gear 25 and in turn drives a sprocket 27. The sprocket 27 is rigidly fixed to a sprocket 28 which drives the chain 23 and this in turn rotates the sprocket l9 fixed on the shaft 18.

The reduction ratio of the variable speed gear 25 is controlled by a shaft 29 which extends through the end plate 5 and carries a handle 30 which is readily accessible just below the left-hand section 8 of the feed table to enable the speed of the conveyor belts 13 to be easily adjusted by a machine operator.

Above the left-hand end of the section 9 of the feed table are four jockey rollers 31 which are mounted on a shaft 32. The shaft 32 is supported at its ends by arms 33 which are fixed on a shaft 34. The shaft 34 is mounted in a bearing 35 fixed to the sideplate 3 and in a similar bearing fixed to the sideplate 2 at its other end. The jockey rollers 31 are thus able to swing upwards and downwards, but they are biased by their own weight and that of the shaft 32 and the arms 33 downwards against the top flights of the conveyor belts l3.

To the right of the crossmember 12 are two electric contacts 36 and 37 which are fixed to blocks 38 and 39 respectively. The blocks 38 and 39 are slidable on rods 40 and 41 respectively and can be fixed in position on these rods by locking screws 42. The contacts 36 and 37 are of springy material and extend downwards through a slot in the guide plate 10 into contact with the section 9 of the feed table in between the two center conveyor belts 13.

To the right of the idler roller 14 is a set of deflecting rollers comprising a roller 43 which is driven from the roller 14 and has a continuous surface and three further rollers 44, 45 and 46 which are each formed from a series of coaxial discs as shown in FIG. 2 and thus having discontinuous surfaces. The discs forming the roller 45 are axially staggered from the discs forming the rollers 44 and 46 so that the surfaces of the rollers can overlap each other as shown in FIG. 1. The roller 43 has stub shafts at its ends mounted in bearings fixed to the sideplate 2 and to a plate 47 which is fixed to the sideplate 43 by lugs 48 but is spaced inwards from the sideplate 3. The discs forming the rollers 44 to 46 are mounted on shafts 49, 50 and 51 respectively which are mounted in bearings 52 on the plate 2 and bearings 53 on the plate 47.

Below the assembly of deflecting rollers 43 and 46 are a pair of rotary creasing devices 54 and 55. The devices 54 and 55 are similar to each other and each includes a driving shaft 56 which is mounted at its ends in bearings 57 and 58 in the sideplates 2 and 3 respectively. Fixed near the ends of the shaft 56 just inside the plates 2 and 47 are rectangular members 59. A male creasing member in the form ofa blade 60 extends between the members 59 and is fixed to them by brackets 61. At the other ends of the members 59 are a fixed bracket 62 and a pivoted bracket 63 which is connected to the member 59 by a pivot pin 64. A pair of creasing rollers 65 and 66, which between them form a female creasing member, extend between the brackets 62 and 63 respectively. The roller 66 which is carried by the pivoted bracket 63 is pressed against the roller 65 by a spring 67.

The rollers 65 and 66 are mounted on shafts which extend through the brackets 62 and 63 which are fixed to that one of the members 59 which is adjacent the sideplate 2 and on the projecting ends of these shafts are meshing pinions 68 and 69 which constrain the rollers 65 and 66 to rotate contra to each other.

At the end of the shaft carrying the roller 65 remote from the pinion 68, this shaft extends through the bracket 62 and through an opening in the plate 47. The shaft terminates between the plate 47 and the sideplate 3 and has a bellcrank lever 70 fixed on its end. The bellcrank lever 70 has arms 71 and 72.

The creasing devices 54 and 55 are rotated by a constant speed electric motor 73 mounted on the bottom plate 6. The motor 73 is fitted with a disc brake to enable it to be stopped so rapidly that the angular position of its rotor can be determined within close limits according to the instant at which the brake is applied. The motor 73 has a pulley 74 driving a belt 75 and this in turn drives a pulley 76 fixed on a shaft 77. The shaft 77 is carried in a bearing on the plate 3 and in a second bearing 78 on the plate 2. The shaft 77 extends through the bearing 78 and carries a sprocket 79 on its end. The sprocket 79 in its turn drives a chain 80 which rotates a sprocket 81 fixed to the shaft 56 of the creasing device 54.

Adjacent the sprocket 81, the shaft 56 of the device 54 has a pinion 82 fixed on it and this pinion meshes with an identical pinion 83 fixed on the shaft 56 of the creasing device 55. Thus the two creasing devices 54 and 55 are rotated at the same speed as each other but in opposite directions as indicated by arrows 84 and 85 shown in FIG. 1.

The shaft 56 of the creasing device 55 extends beyond the bearing 58 and has a cam wheel 86 fixed on its end. The cam wheel 86 has a single protruding hump 87 which operates a microswitch 88 fixed to the outside of the sideplate 3.

The moving parts of the machine which lie outside the sidcplates 2 and 3 are enclosed by covers 89 and 90 respectively which are indicated in chain-dotted lines in FIG. 2.

Below the creasing devices 54 and 55 is a delivery conveyor 91 formed by three conveyor belts 92 the upper flights of which extend over a platform 93. The belts 92 are driven by a roller 94 and they drive a roller 95. The driving roller 94 is rotated by a motor 96 fitted with a reduction gear 97 through a transmission consisting ofa pulley 98, a belt 99 and a further pulley 100 fixed on the shaft of the roller 94. The driven roller drives a delivery roller 101 in a counterclockwise direction as seen in FlG. l by means ofa crossed belt 102.

The machine operates as follows:

Initially the paper feed conveyor belts 13 are driven by the motor 20 at a speed which is determined by adjustment of the gear 25. The delivery conveyor belts 92 and the discharge feed roller 101 are however stationary and so are the rotary creasing devices 54 and 55. The rotary creasing devices 54 and 55 are stopped in the positions shown in FIGS. 1 and 3a of the drawings and this is achieved by the application of the disc brake on the motor 73 by an electric circuit actuated by closure of the microswitch 88 by the hump 87 on the cam wheel 86. Closure of the microswitch 88 also deenergizes the motor 73.

The leading edge of a sheet of paper 103 is then fed manually along the section 8 of the feed table under the guide plate 10 until it enters the nip formed between thejockey rollers 31 and the upper flights of the conveyor belts 13. The sheet 103 is then released and it is conveyed into the machine at the speed determined by the setting of the gear 25. When the leading edge of the paper sheet 103 reaches the contact 36, a circuit through this contact and the section 9 of the feed platform is broken and this actuates a control circuit which starts an electrical timer. After a predetermined time which is adjusted by an interconnection between the timer and the shaft 29 which adjusts the speed of the conveyor 13, a further circuit is closed which releases the disc brake of the motor 73 and energizes the motor so that the rotary creasing devices 54 and 55 start to rotate. The time delay is provided to allow the leading part of the sheet 103 to move between the creasing devices 54 and 55 before these are set in operation so that the first crease in the sheet 103 is made at the required distance from the leading edge of the sheet. The contact 36 is made adjustable in position to permit a fine adjustment to be made in the position of the crease. The contact 36 is set in conjunction with an adjustment of the timer to allow the first crease to be accurately located.

The time delay is adjusted in dependence upon the speed of the conveyor belts 13 and on the speed of rotation of the devices 54 and 55, which is constant, so that the blade 60 comes into contact with the sheet 103, the leading end of which has by this time been fed into the position shown in FIG. 1. At the same time the roller 65 on the device 55 comes into contact with the other side of the sheet and the blade 60 pushes a portion of the sheet into the nip formed between the rollers 65 and 66 of the device 55.

As the rollers 65 and 66 of the device 55 approach the 9 oclock position shown in FIG. 3b, the arm 71 of the bellcrank lever 70 strikes a pin 104 which projects inwards from the sideplate 3. As the device 55 continues to rotate in a counterclockwise direction towards the 9 oclock position, the pin 104 turns the bellcrank lever 70 in a clockwise direction thus causing the roller 65 to rotate clockwise and the roller 66 to rotate counterclockwise. At this happens the blade 60 of the device 54 advances further into the nip between the rollers 65 and 66 of the device 55 which are thus moved slightly apart against the action of the spring 67. The paper sheet 103 is moved into the nip between the blade 60 and the rollers 65 and 66 and further rotation of the rollers 65 and 66 causes the paper to be drawn further into the nip away from the tip of the blade 60 as the device 55 turns further in counterclockwise direction and as the blade 60 is withdrawn from between the rollers, they are forced together with only the paper sheet between them by the spring 67 so that the paper sheet is sharply creased. The blade 60 of the device 54 and the rollers 65 and 66 of the device 55 then separate as the devices reach a position between the positions shown in FlGS. 3b and 3c and the paper sheet 103 with a single crease in it continues to be fed on by the conveyors belts 13 in between the devices 54 and 55. As the device 55 approaches the position shown in FIG. 30 the arm 72 of the bellcrank lever 70 strikes a further pin 105 shown in FIG. 30 and this causes the rollers 65 and 66 to be rotated in counterclockwise and clockwise directions respectively so that the creased part of the paper sheet 103 is discharged from the nip between the rollers. After this the sheet is then trapped between the blade 60 of the device 55 and the rollers 65 and 66 of the device 54 and the arm 71 of the bellcrank lever 70 of the device 54 strikes a pin 106 causing the rollers 65 and 66 of the device 54 to rotate and exactly the same operation then takes place with the device 54 as that already described for the device 55. However, with this operation the paper sheet 103 is creased in an opposite direction. In the course of this operation the arm 72 of the device 54 strikes a pin 107 as shown in FIG. 3a and this causes the creased part of the sheet to be discharged by the device 54.

These operations continue as feeding of the sheet by the conveyor belts 13 takes place and thus the sheet is creased alternately in opposite directions as spaces along its length which are dependent upon the speed of the conveyor 13.

If the sheet 103 were fed through the machine by the conveyor belts 13 and the roller 43 until the trailing edge reached the roller 43, there would be a great likelihood of the part of the sheet near the trailing edge falling from the roller 43 in between the devices 54 and 55 so that the last crease in the sheet was not made and the final panel was larger than those preceding it. It is to prevent this that the contact 37 is provided.

When the trailing edge of the sheet 103 passes the contact 37, an electrical circuit is completed from this contact through the section 9 of the feed table. The completion of this circuit energizes a control circuit which switches off the motor 20 and thus stops both the conveyor belts 13 and the roller 43. The trailing portion of the sheet 103 thus remains lightly held between the roller 43 and the rollers 44 and 46. It cannot therefore fall down freely between the devices 54 and 55. As the trailing portion of the sheet is gripped between one of the blades 60 and one of the pairs of rollers 65 and 66, it is creased and fed onwards, but by a distance less than it would be fed by the conveyor 13 during one half turn of the devices 54 and 55. This onward movement draws the trailing edge of the sheet 103 from between the rollers 43 and 44 to 46 and it then drops down. In this way the last panel of the folded sheet is smaller than the remaining panels and the last but one panel may also be smaller in dependence upon the distance by which the sheet has been fed from the preceding fold up to the time that the contact 37 completes the control circuit.

When the trailing edge of the sheet 103 passes the contact 36, the circuit through this contact is remade and after a further time delay this causes the motor 73 to be switched off and its disc brake to be applied when next the switch 88 is closed by the cam hump 87. This brings the devices 54 and 55 to rest in the positions shown in F 1G. 1 ready for the feeding in of the next sheet. The second time delay is necessary to ensure that the creasing devices 54 and 55 do not stop until the last crease has been formed in the sheet 103 and the sheet can fall freely on to the conveyor belts 92.

The closure of the switch 88 subsequent to the remaking of the circuit through the contact 36 also operates a control circuit which starts the motor 96 so that the folded sheet lying on the conveyor belts 92 as shown in FIG. 1 at 103a, is fed by the conveyor belts 92 out of the righthand side of the casing l. The ejection of the folded sheet is assisted by the roller which presses the top of the folded sheet 103a downwards and helps to move it onwards.

In an alternative mode of operation, the conveyor belts 92 are set in operation as soon as the machine is switched on and in consequence the sheet is fed out of the machine as it passes onwards through the creasing devices 54 and 55. It does not then collapse into its concertina formation shown at 103a until it has left the machine and has been discharged by the conveyor belts 92 onto a discharge platform.

lclaim:

l. A machine for folding a sheet with a concertina fold, said machine including a pair of rotary creasing devices, means rotatably mounting said creasing devices in side-by-side relationship for rotation in directions contra to each other and means for feeding said sheet to be folded freely between said pair of rotary creasing devices, each of said creasing devices including a male creasing member and a female creasing member, each of said male creasing members including axially extending blade means and each of said female members including a pair of rollers, means mounting said rollers parallel to and in contact with each other whereby said rollers form a nip between them, said nip of said one creasing device being arranged to receive said blade of said other creasing device and vice versa as said creasing devices rotate, said rollers being of a diameter which is relatively small compared with the diameter of a pitch circle around which said rollers move as said creasing device rotates and said nip extending parallel to the axis of rotation of said device, and driving means for intermittently rotating said pair of rollers as said device rotates, said intermittent driving means including a pair of pinions, means fixing said pinions one to each of said rollers for rotation therewith, means mounting said pinions in meshing relationship with each other, a pair of arms, means fixing said arms to each other to form a bellcrank lever, means rigidly connecting said bellcrank lever to one of said rollers with said arms projecting radially therefrom, a pair of pins and means stationarily mounting said pins in the paths of said arms as said devices rotate whereby one of said arms of said bellcrank lever strikes one of said pins as said device rotates to rotate said roller which is rigid therewith in one direction, said other roller being rotated in a contra direction by said meshing pinions and said other arm of said bellcrank lever subsequently strikes said other pin to rotate said rollers in opposite directions whereby said sheet is drawn into said nip as said rollers on one of said creasing devices mate with said blade on the other of said creasing devices and subsequently said sheet is released as said rollers rotate in said opposite directions so that said creasing devices produce creases alternately in opposite directions in said sheet fed between said devices by said feeding mechanism, and means for adjusting the speed of said feeding mechanism and the rate of rotation of said devices relatively to each other whereby the spaces between adjacent creases in said sheet, which are dependent upon the rate of feed of said sheet relative to said rate of rotation of said devices, may be varied.

2. A machine as claimed in claim 1, further comprising means mounting one of said rollers of said pair for rotation about an axis which is fixed relative to said device, means mounting the other roller of said pair about an axis of rotation which is laterally movable relative to said device and spring means for pressing said other roller of said pair against said one roller of said pair.

3. A machine as claimed in claim 1, further comprising drive means for rotating said rotary creasing devices at constant angular speeds and variable speed drive means for driving said feed mechanism, said variable speed drive means forming said means for adjusting the speed of said feed mechanism and the rate of rotation of said devices relative to each other.

4. A machine as claimed in claim 3, wherein said variable speed drive means includes a constant speed electric motor, a variable speed gear, means operatively connecting said motor to said gear and means operatively connecting said gear to said feed mechanism.

5. A machine as claimed in claim 1, wherein said feed mechanism includes endless conveyor belt means, jockey roller means and means biasing said jockey roller means towards said conveyor belt means for pressing said sheet against said belt means.

6. A machine as claimed in claim 1, wherein said creasing devices are mounted with their axes of rotation horizontal and said feed mechanism is arranged to feed said sheet horizontally and said mechanism further includes an assembly of deflection rollers and means mounting said rollers for receiving said sheet fed horizontally by said feed mechanism and deflecting it vertically downwards between said creasing devices. 7

' 7. A machine as claimed in claim 1, further comprising conveyor belt means, and means mounting said conveyor belt means horizontally below said creasing devices for delivering said sheet after creasing out of said machine.

8. A machine as claimed in claim 1, further comprising retarding means and means operatively connecting said retarding means to said creasing, devices for bringing said creasing devices to rest in preset angular positions, said feed mechanism including sensing means for sensing the position of the leading edge of said sheet as it is fed by said feeding mechanism towards said creasing devices, means for setting said creasing devices in rotation from said preset position and means connecting said sensor to said means for setting said creasing devices in rotation, said connecting means including time delay means wherein said creasing devices start to rotate a preset time after said leading edge of said sheet has reached said sensing means, said preset time being dependent upon the speed of said feed mechanism whereby said sheet has a first crease formed therein by said creasing means at a predetermined distance from said leading edge of said sheet.

9. A machine as claimed in claim 8, further comprising second sensing means for sensing the position of the trailing edge of said sheet after said sheet has passed through said feed mechanism, said second sensing means being operatively connected to said feed mechanism whereby said feed mechanism is stopped when said trailing edge reaches said second sensing means, said sheet thereafter being moved onwards by said creasing devices whereby the distance between a last crease formed in said sheet and said trailing edge of said sheet is no greater than the distance between adjacent preceding creases in said sheet. 

1. A machine for folding a sheet with a concertina fold, said machine including a pair of rotary creasing devices, means rotatably mounting said creasing devices in side-by-side relationship for rotation in directions contra to each other and means for feeding said sheet to be folded freely between said pair of rotary creasing devices, each of said creasing devices including a male creasing member and a female creasing member, each of said male creasing members including axially extending blade means and each of said female members including a pair of rollers, means mounting saId rollers parallel to and in contact with each other whereby said rollers form a nip between them, said nip of said one creasing device being arranged to receive said blade of said other creasing device and vice versa as said creasing devices rotate, said rollers being of a diameter which is relatively small compared with the diameter of a pitch circle around which said rollers move as said creasing device rotates and said nip extending parallel to the axis of rotation of said device, and driving means for intermittently rotating said pair of rollers as said device rotates, said intermittent driving means including a pair of pinions, means fixing said pinions one to each of said rollers for rotation therewith, means mounting said pinions in meshing relationship with each other, a pair of arms, means fixing said arms to each other to form a bellcrank lever, means rigidly connecting said bellcrank lever to one of said rollers with said arms projecting radially therefrom, a pair of pins and means stationarily mounting said pins in the paths of said arms as said devices rotate whereby one of said arms of said bellcrank lever strikes one of said pins as said device rotates to rotate said roller which is rigid therewith in one direction, said other roller being rotated in a contra direction by said meshing pinions and said other arm of said bellcrank lever subsequently strikes said other pin to rotate said rollers in opposite directions whereby said sheet is drawn into said nip as said rollers on one of said creasing devices mate with said blade on the other of said creasing devices and subsequently said sheet is released as said rollers rotate in said opposite directions so that said creasing devices produce creases alternately in opposite directions in said sheet fed between said devices by said feeding mechanism, and means for adjusting the speed of said feeding mechanism and the rate of rotation of said devices relatively to each other whereby the spaces between adjacent creases in said sheet, which are dependent upon the rate of feed of said sheet relative to said rate of rotation of said devices, may be varied.
 2. A machine as claimed in claim 1, further comprising means mounting one of said rollers of said pair for rotation about an axis which is fixed relative to said device, means mounting the other roller of said pair about an axis of rotation which is laterally movable relative to said device and spring means for pressing said other roller of said pair against said one roller of said pair.
 3. A machine as claimed in claim 1, further comprising drive means for rotating said rotary creasing devices at constant angular speeds and variable speed drive means for driving said feed mechanism, said variable speed drive means forming said means for adjusting the speed of said feed mechanism and the rate of rotation of said devices relative to each other.
 4. A machine as claimed in claim 3, wherein said variable speed drive means includes a constant speed electric motor, a variable speed gear, means operatively connecting said motor to said gear and means operatively connecting said gear to said feed mechanism.
 5. A machine as claimed in claim 1, wherein said feed mechanism includes endless conveyor belt means, jockey roller means and means biasing said jockey roller means towards said conveyor belt means for pressing said sheet against said belt means.
 6. A machine as claimed in claim 1, wherein said creasing devices are mounted with their axes of rotation horizontal and said feed mechanism is arranged to feed said sheet horizontally and said mechanism further includes an assembly of deflection rollers and means mounting said rollers for receiving said sheet fed horizontally by said feed mechanism and deflecting it vertically downwards between said creasing devices.
 7. A machine as claimed in claim 1, further comprising conveyor belt means, and means mounting said conveyor belt means horizontally below said creasing devices for delivering said sheet aftEr creasing out of said machine.
 8. A machine as claimed in claim 1, further comprising retarding means and means operatively connecting said retarding means to said creasing devices for bringing said creasing devices to rest in preset angular positions, said feed mechanism including sensing means for sensing the position of the leading edge of said sheet as it is fed by said feeding mechanism towards said creasing devices, means for setting said creasing devices in rotation from said preset position and means connecting said sensor to said means for setting said creasing devices in rotation, said connecting means including time delay means wherein said creasing devices start to rotate a preset time after said leading edge of said sheet has reached said sensing means, said preset time being dependent upon the speed of said feed mechanism whereby said sheet has a first crease formed therein by said creasing means at a predetermined distance from said leading edge of said sheet.
 9. A machine as claimed in claim 8, further comprising second sensing means for sensing the position of the trailing edge of said sheet after said sheet has passed through said feed mechanism, said second sensing means being operatively connected to said feed mechanism whereby said feed mechanism is stopped when said trailing edge reaches said second sensing means, said sheet thereafter being moved onwards by said creasing devices whereby the distance between a last crease formed in said sheet and said trailing edge of said sheet is no greater than the distance between adjacent preceding creases in said sheet. 